Fix problems with lazy vals and separate compilation

Somehow this error manifested itself in a quite weird way during erasure.
So it was hard to track down

Author: DarkDimius

src/dotty/tools/dotc/transform/LazyVals.scala

@@ -27,7 +27,8 @@ class LazyVals extends MiniPhaseTransform with SymTransformer {
 
 
   def transformSym(d: SymDenotation)(implicit ctx: Context): SymDenotation = {
-    if(d is(Flags.Lazy, butNot = Flags.ModuleVal)) {
+    if(d is(Flags.Lazy, butNot = Flags.ModuleVal | Flags.Method)) {
+      // Method flag is set on lazy vals coming from Unpickler. They are already methods and shouldn't be transformed twice
       d.copySymDenotation(
         initFlags = d.flags | Flags.Method,
         info = ExprType(d.info))

tests/pos/lazyValsSepComp.scala

@@ -0,0 +1,16 @@
+package dotty.tools
+package io
+
+import java.io.{ InputStream }
+import java.util.jar.JarEntry
+import dotty.tools.dotc.core.Definitions
+import language.postfixOps
+import dotty.tools.dotc.core.Contexts._
+
+
+/** A test to trigger issue with separate compilation between Dotty and Scalac and lazy vals */
+object Foo {
+  val definitions: Definitions = null
+  def defn = definitions
+  def go = defn.FunctionClass(0)
+}